Light emitting diodes (LEDs) having advantages, such as high light emission efficiency, high luminance, and electric power saving, have been widely utilized as light sources for vehicle lighting fixtures, such as turn signal lamps, rear lamps, stop lamps, etc. to be disposed on left and right sides of the rear portion of a vehicle body. Such an LED can emit light with strong directivity. Thus, in such a vehicle lighting fixture using the LED, the light with strong directivity is tried to be guided through a light guiding body so that the entire light guiding body can project light (the entire light guiding body can be illuminated with light). Specifically, such a light guiding body can project light (can be illuminated with light) by means of the following mechanism. That is, a light source can be disposed to face to the light guiding body with its incident surface opposed to the light source, and the light emitted from the light source can enter the light guiding body through the incident surface to an opposite side of the light guiding body to the incident surface side. Since the light guiding body can include a reflecting portion formed on a back surface, when the light having entered the light guiding body is guided (travels) through the light guiding body, part of the light can be totally reflected by the reflecting portion on the back surface to thereby be projected through a front surface of the light guiding body. In this manner, the light can be projected through the entire front surface of the light guiding body (the light guiding body can be entirely illuminated with the light through the front surface).
A conventional vehicle lighting fixture using a light guiding body will be described on the basis of FIGS. 1 and 2.
FIG. 1 is a front view of a conventional vehicle lighting fixture 101 and FIG. 2 is a cross-sectional view of the vehicle lighting fixture 101 taken along line B-B in FIG. 1. The illustrated vehicle lighting fixture 101 can be used as a turn signal lamp to be disposed on left and right sides of a vehicle body.
As illustrated in FIG. 2, the vehicle lighting fixture 101 to be used as a turn signal lamp can include a housing 102 having an opening and a transparent outer lens 103 configured to cover the opening of the housing 102 to define a lighting chamber 104. The vehicle lighting fixture 101 can further include a plurality of LEDs 105 (five LEDs in the illustrated example) as light sources, a light guiding body 106, an extension 107, etc., which are housed in the lighting chamber 104.
The vehicle lighting fixture 101 can further include an elongated substrate 108 which is disposed laterally (in a left-right direction in FIG. 1) at the upper portion within the lighting chamber 104 and on which the plurality of LEDs 105 are mounted at predetermined intervals so that the LEDs 105 can emit light downward.
The light guiding body 106 can be formed in a plate shape from a transparent resin such as an acrylic resin or a polycarbonate resin having light-guiding properties. The light guiding body 106 can include an incident surface 106a facing to the LEDs 105 at its upper surface and a light exiting surface 106b at its front surface. Furthermore, as illustrated in FIG. 2, the light guiding body 106 can be formed to be stepwisely thinned from a side of the incident surface 106a to its lower end side (an opposite side to the incident surface). In the illustrated example, there can be formed three reflecting portions 106c each having a reflecting surface at respective boundary portions of a rear surface of the light guiding body 106 where the thickness of the light guiding body 106 is stepwisely changed as illustrated in FIGS. 1 and 2. The reflecting portions 106c can be parallel with each other in the vertical direction while being curved obliquely rightward and upward in FIG. 1.
In the illustrated example, the housing 102 and the extension 107 can be integrally formed by an opaque resin that cannot transmit light so that the extension 107 can cover the LEDs 105, the substrate 108, and peripheries of the light guiding body 106.
In the vehicle lighting fixture 101 with the above-described configuration, when the plurality of LEDs 105 are supplied with a current to emit light, the light emitted downward from the LEDs 105 can enter the light guiding body 106 through the incident surface 106a of the light guiding body 106 as illustrated in FIG. 2. Then, as the light having entered the inside of the light guiding body 106 can travel (be guided) downward, part of the light can be totally reflected by the respective reflecting surfaces of the reflecting portions 106c formed in the rear surface of the light guiding body 106 to the front surface side (leftward in FIG. 2). Thus, the reflected light can be projected through the light exiting surface 106b and then through the transparent outer lens 103 forward, so that the three reflecting portions 106c of the light guiding body 106 can be observed as being illuminated with light in a curved manner when viewed from its front side.
Furthermore, Japanese Patent Application Laid-Open No. 2008-097923 proposes a vehicle lighting fixture using a light guiding body, which is illustrated in FIGS. 3 and 4.
FIG. 3 is a perspective view of the light guiding body 206 used in the vehicle lighting fixture proposed in Japanese Patent Application Laid-Open No. 2008-097923, and FIG. 4 is a front view illustrating an optical path within the light guiding body 206 of FIG. 3. The light guiding body 206 includes a first light guiding portion 206A, a light inverting portion 206B, a second light guiding portion 206C, and a light reflecting portion 206D.
Specifically, the first light guiding portion 206A can include an incident surface 206a at its longitudinal end to be opposed to a not-illustrated light source. The light inverting portion 206B is formed at an opposite longitudinal end of the first light guiding portion 206A and the second light guiding portion 206C. The light inverting portion 206B includes two inclined reflecting surfaces 206b and 206c so as to provide a function of inverting the traveling direction of parallel light rays guided from the first light guiding portion 206A.
The second light guiding portion 206C is thinned from the opposite longitudinal end side, and the light reflecting portion 206D is formed on the entire rear surface of the second light guiding portion 206C in the longitudinal direction by forming a plurality of triangular prism cuts disposed side by side in the longitudinal direction.
In the light guiding body 206 with the above-described configuration, when the not-illustrated light source is turned on to emit light, the light can enter the light guiding body 206 through the incident surface 206a of the first light guiding portion 206A to travel through the first light guiding portion 206A to the light inverting portion 206B. Then the light can be totally reflected by the reflecting surfaces 206b and 206c of the light inverting portion 206B to invert the traveling direction by 180°. The light travelling in the inverted direction through the second light guiding portion 206C can be reflected by the light reflecting portion 206D to be projected through the front surface (light exiting surface) of the second light guiding portion 206C. Thus, when observed from its front side, the light reflecting portion 206D can be observed as being illuminated with light.
Problems in association with such conventional techniques will now be discussed.
In the vehicle lighting fixture 101 illustrated in FIGS. 1 and 2, the light with strong directivity from the respective LEDs 105 as represented by L1 in FIG. 1 can travel downward through the light guiding body 106 while being diffused in a triangular front shape. Such light L1 directly reaching the respective reflecting portions 106c can be totally reflected by the respective reflecting portions 106c to be projected through the front light exiting surface 106b. In this case, the light L1 cannot reach the parts of the reflecting portions 106c of the light guiding body 106 closer to the LEDs 105, so that the reflected light rays can be separately projected and thus darkened portions may be generated (occurring uneven illuminance). Incidentally, it is difficult to dispose LEDs 105 on the opposite side (lower side in the drawings) from the viewpoint of general problems in association with processing vehicle bodies.
In the light guiding body 206 illustrated in FIGS. 3 and 4, since the light travelling through the first light guiding portion 206A is returned by the light inverting portion 206B (the travelling direction is inverted), the light guiding body 206 can project light as if the light source is disposed on the opposite side to the actual disposition side. However, the light can be projected only from the light reflecting portion 206D of the second light guiding portion 206C and the light guiding body 206 is thick by the thickness of the first light guiding portion 206A, resulting in enlarged size of the entire light guiding body 206. Specifically, as illustrated in FIG. 4, the light guiding body 206 has a thickness t being constant in the longitudinal direction while the light projecting portion or the second light guiding portion 206C has a half of the thickness t.